Climbing into Opposite Traffic on an RVSM Airway
At 1420 UTC, Nairobi Control has KQA 200, a B787, maintaining FL330 on airway UB535 eastbound, requesting FL370 because of moderate turbulence. Traffic: ET-AXA, a B738, maintaining FL370 on the same airway westbound, 120 NM ahead, Mach 0.78. KQA 200 is Mach 0.84. The sector is RVSM airspace; the next adjacent sector boundary is 80 NM ahead and the crew advises turbulence is increasing. A military restricted area R-204 is active 30 NM to the south, so a large lateral diversion is not desirable. A third aircraft, a Cessna Citation at FL350, is 60 NM behind KQA 200, also eastbound, requesting FL380. You have no direct radar coverage beyond 40 NM but have ADS-C position reports.
1. Can you approve KQA 200's climb to FL370? Show the conflict logic.
Read the worked answer
No. ET-AXA is opposite direction at FL370, 120 NM ahead, and KQA 200 is requesting the same level. Closing speed is roughly Mach 0.84 plus Mach 0.78, about 900 kt, so the aircraft would be in the same vertical window in approximately eight minutes if the climb were started now. RVSM permits 1,000 ft vertical separation, not same-level opposite direction. The fact that KQA 200 might reach FL370 before ET-AXA passes does not make it safe: the two aircraft would then be head-on at the same level. In addition, the Citation is behind at FL350, so a climb through FL350 must be coordinated. The correct decision is to deny FL370 for now and offer an interim level.
2. Give a safe interim plan using the available levels and traffic.
Read the worked answer
Climb KQA 200 to FL340 initially. FL340 is 3,000 ft below ET-AXA at FL370 and 1,000 ft below the Citation at FL350, so vertical separation is maintained. Advise KQA 200 that FL370 is not available due to opposite traffic and that a further climb can be expected after ET-AXA passes. Keep the Citation at FL350 for the moment. Do not clear KQA 200 to FL360 or FL370 until ET-AXA has passed and you have positive assurance of separation; FL360 would be only 1,000 ft below ET-AXA and would increase the risk if either aircraft deviates in turbulence. Reassess after ET-AXA is clear, then coordinate KQA 200 to FL370 and the Citation to FL380 as traffic allows.
3. How do you handle the Citation's request for FL380?
Read the worked answer
Do not approve FL380 while ET-AXA is at FL370 opposite direction. The Citation at FL350 would have to climb through FL370 to reach FL380, which would cross the opposite traffic's level. Approve FL360 instead if the Citation can accept it: FL360 does not require crossing FL370 and keeps 1,000 ft below ET-AXA, while maintaining 2,000 ft above KQA 200 at FL340. If FL360 is not acceptable, instruct the Citation to maintain FL350 and advise when FL380 can be expected. Record the coordination and ensure the next controller knows the sequence: KQA 200 at FL340, Citation at FL360 or FL350, ET-AXA passing at FL370.